Question about Nexium and Bentyl

Over the past several months I have been having excessive amounts of gas, constipation, diarrhea, nausea, etc. They vary in severity from day to day, some days are better than others. When I wake up in the morning I have to use the restroom almost immediately, and then 20-30 minutes after I'm done I feel like I need to go again, and sometimes again after that. Even when I don't have to go I feel sick most of the time.

Anyways, I went to my primary doctor and told her all these things (in much better detail) and she prescribed me Bentyl 20mg which I took for a few weeks. It had little to no effect on my symptoms, which was really frustrating and I stopped taking it. I called my doctor back and she referred me to a gastroenterologist who in turn prescribed me Nexium. My dad takes Nexium because he has heartburn and trouble swallowing, so I was surprised when this medicine was prescribed to me when our symptoms are completely different. I made sure to tell the specialist that I didn't really have heartburn, that my primary concern was all the gas, diarrhea, and frequent trips to the bathroom.

I'm not questioning my doctors credibility but I'm just a little worried that this medicine isn't going to help me. Can anyone shed some light on exactly what Nexium can be used for and if it is going to help alleviate the symptoms I am experiencing ?